A Philadelphian pronunciation of the word "joint."
This now means almost any thing, usually used in place of an object, the name of which either can't be currently remembered or needs to be obscured. It conforms to a similar definition of slang in the word "piece", although, in reference to weed, a joint is a joint, a piece is a piece.
It should be noted, as it is here many times, the word has come to be used in slang through African-American culture, mostly from use in the East Coast, and generally referring to artistic ventures (a movie, song, or some other project).